[linux-lvm] lvchange -r 256 lv-name does not work

From: Sachin Sant <sachinp in ibm com>

To: linux-lvm sistina com

Subject: [linux-lvm] lvchange -r 256 lv-name does not work

Date: Thu Nov 27 07:48:05 2003

Hi , i came across a problem with lvchange command.
I have a VG with 3 pv and a lv created using command
lvcreate -i3 -I32 -l98 -nmy_lv my_vg
lvdisplay shows 1024 as the value for Read Ahead Sectors.
When i use the command lvchange to change the value of read ahead
sector with value more that or equal to 256 i get following error..
linux# lvchange -r 340 /dev/my_vg/my_lv
lvchange -- ERROR "Invalid Argument" read ahead sector change
linux#
linux#
After debugging i found that in drivers/block/blkpg.c file blk_ioctl( )
Case BLKRASET :
if (arg > 0xff )
return -EINVAL;
Effectively this does not allow value greater that 255 for read ahead.
Is there a limitation that the read ahead sectors can't have value more
than 255 ? If yes then why lvdisplay shows 1024 as the default value for
read ahead sectors.
Thanks
-Sachin